Spark plug



Jan. 7, 1930, H. RABl-:zzANA S PARK PLU G Filed NOV. 12, 1924 if i;

Patented Jan. 7, 1930 E 'Il FFE HECTOR RABEZZANA, OF FLINT, MICHIGAN, ASSIGNOR T0 A C SPARK PLUG COMPANY,

OF FLINT, MICHIGAN, A COMPANY 0F INH(LHIZ'AN'` SPARK PLUG Application led November 12, 1924. Serial No. 749,414.

My invention relates to spark plugs designed for use with internal combustion engines to ignite the combustible mixture supplied to and burned within the working c lin- 5 der thereof, and the principal object o the invention is to provide a spark plug having features of construction and arrangement of parts such that heat may flow from the insulating member of the plug to the shell or casing, and from thence to cylinder wall er head of the engine more readily, that is, with less resistance to such flow of heat, than has heretofore been the case; to the end or with. the result that the plug, and particularly the insulating member thereof, will remain cooler than has heretofore commonly been the case. Any reduction in temperature of the insulating member, particularly at the exposed inner end thereof, secured in a spark plug lessens the tendency to pre-ignition of the mixture durin the compression thereof in the engine cylin er; and the more free flow of heat from the inner end of the plug secured in my improved spark plug lessens the tendency to preignition when the engine is in operation. My improved spark plug is especially adapted for use in racing automobiles the engines of which when driven at their maximum capacity operate -much hotter than is ordinarily the case in automobile engines, and in which service pre-ignition of the mixture is particularlv liable to occur. As a matter of fact pre-ignition of the mixture is ordinarily the most serious difficulty met with, and the most prominent single circumstance operating to limit the temperature of operation of an internal combustion engine.

A further object of my invention is to provide a spark plug wherein the inner end of the insulating member which -is exposed to the burning gases will be less liable to become cracked or broken, due to strains resulting from expansion of said inner end when the plug is in operation, than in prior plugs; such expansion being obviously the more pronounced, and the harmful results thereof the more diflicult to avoid and overcome in cases where the plug is used in an engine designed to operate at an inordinately high temperature,

A further object of my invention is to provide a spark plug which will be more nearly gas tight, andin which there will be less leak.- age between the insulating member and the shell and central electrode than heretofore; and other and further objects and advantages of my invention will be pointed out in the more full and complete explanation thereof hereinafter appearing.

rlhe drawing accompanying and forming a part of this specilication illustrates the preferredV embodiment of my invention; al though the same may be embodied in. various other forms, all of which regard as included in my invention and in the patent to be secured therefor so long as such variations and modifications come within the scope 0f the concluding claims; wherein the distinguishing features of my invention are particularly pointed out In the drawing:

Figure l is a View showing a spark plug made in accordance with my invention upon a' central thereof.

Figure 2 is a View showing a section upon a transverse plane indicated by the line 2 2', Figure 1, looking down.

Figure 3 is a view similar to Figure 1 but showing my invention as slightly modified as regards certain parts and features thereof.

Figure 4 is a view showing a section upon a transverse plane indicated by the line fle-4, Figure 3, looking down.

Referring now to the drawing, the reference numeral 5 designates the external metallic shell or casing of my improved spark plug, the same having a threaded portion 6 which screws into a threaded opening in the cylinder Wall or head of the engine with which the plug is used; said casing being hollow to provide a passage within which the insulating member 7 of the plug is held in any suitable way7 as by an inturned flange 8 at the outer end of the shell which overlies a shoulder adjacent the upper end of the insulating member.

The passage within which the insulating plane extending longitudinally member is located is shown as comprising an upper cylindrical portion 9 and a lower coniof joint between the offer a minimum ofre'sistance to the fiowof cal portion 10, and the insulating member as having correspondingly shaped portions as shown. The lower conical portion of the insulating member and the conical portion 10 of the passagein the casing are ground surfaces, in order to secure intimate contact between the two throughout a joint of large area; the final fitting of the parts to one another being preferably4 accomplished by. grinding (rotating) each particular insulating member in place within the shell with which it is to be used.

The comparatively extensive and large area parts thus secured, together with the intimate contact between the parts clue to the grinding. provides a joint which offers a minimum of resistance to the ow of heat from the inner end of the insulating member and central electrode of the plug (designated by the numeral 11) to the casing thereof, and to the wall of the engine cylinder; -and provides va plug which will operate cooler, and with less liability to reignition of the mixture than has hereto ore commonly been the case. Obviouslythis result is dependent more upon the conical than upon the cylindrical portion of the passage, within which the insulating member is contained; and the relative lengths of these parts may be varied to a point where the cylindrical portion disappears, withta concomitant reduction in the resistance to the How of heat from the insulating member to the shell and to the engine cylinder. Furthermore, and as will be appreciated, the joint formed as aforesaid between the conical portion of the insulating member land the seat wherein it rests is one which will be unusually tight, and one wherein leakage of gas therethrough will be effectively prevented; and that without the use of a gasket adjacent the inner end of the insulating member such as has heretofore usually been used inspark plugs.

The central electrode 11 extendsthrougnh a passage provided in the insulating mem er, and termlnates adjacent the grounded or shell electrode 12 ofthe plug as heretofore. Said electrode, however, is made more massive than is usually the case, and is threaded ani screwed into a roughly threaded portion Af the passage along which it extends; the

threads being coated with a suitable cement before the electrode is screwed into place in order to securea gas tight joint and a more intimate contact between the parts which will heat from the central electrode to the insu- Vthe parts when t the plug. The central electrode may have threaded en d portions with an intermediate unthreaded portion as shown in Figure l, or may be threaded throughout its entire length as shown in'Figure 3. Both forms appear to be equally effective, although the latter is somewhat to be preferred as a manufacturing Y proposition.

The inner end of the insulating member which is exposed to the heat of the burning gases is provided with a conical chamber 13 the wall of which is inclined oppositely to the wall of the conical shell passage 10, and the inner end 14 of the insulated electrode 11 lies within this chamber in the assembled plug. This construction provides the usual dead gas chamber commonly present in spark plugs to prevent short circuiting at the spark gap; although it will be appreciated that the chamber herein is surrounded by an insulating wall provided by the lower end of the insulating member which feature secures a higher temperature at the spark gap, and a more effective burningaway of carbon, oil, etc. from the terminals at the gap, than is the case in spark plugs wherein the outer wall of the dead gas chamber isa metallic wlall integral with the shell or casing of the p ug. i

In order to prevent breaking or cracking of the inner end of the insulating member where its cross section is considerably reduced to provide the dead gas chamber 13 I reduce the vdiameter of said inner end slightly, as by 4grinding a circumferentially extending recess about such inner end, as indicated at 15 in Figures 1 and 2; the Figure 3 and 4 forms `not having such a recess 'as the plug will operate satisfactorily without such a recess when the same is used in engines wherein excessively high temperatures are not likely to occur. Plugs having such recesses are,

however, preferred in services wherein excessive heating is to be expected, as in racin cars as herembefore explained.

The purpose of the recess 15 as explained is primarily to preventbreaking of the inner end of the insulating member by stresses resulting from ex ansion and contraction of iie plug is subjected to inor-A dinately high temperature, as hereinbefore explained, which it does by providin a sort of cushion between the parts which w1ll yield under the stresses due to expansion and contraction of the parts, even though the recess may become more or less filled with carbon deposited by the burning gases. Said recess, however, performs the further. function of reducing the flow of heat from the chamber 13 to the metallic casing of the `plug and to the cylinder wall, and thus secures a higher temperature and a more effective burning away of carbon deposit at the spark gap. As a matter of course such heat as cannot be confined to the vicinity of the gap, and which cannot be prevented from flowing along the central electrode and insulating member, iows along said parts and is the more effectively dissipated by the various parts and features of the improved plug wherein my invention consists, as has hereinbefore been explained in detail.

Having thus described and explained my invention, I claim and'desire to secure by Letters Patent:

In a spark plug, al unitary single piece hollow metallic shell or casing having an interior insulator receiving passage conical in form, and which passage is of least area at the inner end of the casing and becomes larger as the distance from said inner end increases; an insulating member formed separately from said shell and ground in place therein, and having a tapering portion which lits within said passage and extends substantially to the inner end of said casing and which member is secured in place within said passa-ge b an inturned flange at the upper end of said s ell, said member havin a chamber conical in form in its inner en and the Wall of which chamber is inclined opposite to the inclination of the adjacent conical wall of the casing aforesaid; an insulated electrode extending through a centrally arranged vpassage in said insulating member and into said conical chamber; and a grounded or shell electrode carried by said external casing and arranged in sparking relation to the inner end of said insulated electrode.

In testimony whereof I aix m signature. y

HECTOR RAB ZZANA. 

